This is not wasted effort and you are not enabling those who litter. Such individuals are simply oblivious to the blight on the landscape they create through their thoughtless acts, so they will not notice that you or some mysterious figure is making improvements and thereby alert them or perhaps shame them into being more respectful. They simply give no thought to the consequences of discarding anything no longer wanted. They are insensitive to environmental beauty to a significant degree and that is why they carry out such acts. They are not bothered by seeing trash from others that to many is a visible blight and quite disheartening. This is simply a symptom of the human condition, that people are quite beaten down by life and many sources of disparagement, all of which cause them to be increasingly disconnected from their divinity and the divine impulses that bring reminders of love, joy, and beauty in all things. So in a sense, it is a measure of divine alignment.
Your act of generosity in restoring beauty is a blessing and an act of loving kindness that you can rightly feel pride about and know that Gaia and the rest of the human community who are still in divine alignment will recognize and be grateful. In a sense, everyone who looks at a beautiful river landing and sees the natural beauty despite its proximity to human civilization will have an inner thrill from a connection to the divine that otherwise would be besmirched and perhaps short-circuited by seeing ugliness of trash present but for your efforts at cleanup. That moment of love entering them will change them and will uplift and will in some small way alter their life trajectory. This will be repeated again and again and will be owing to your loving stewardship of the environment and will bring rewards in the future to you.
Many will benefit from your actions and while they may not know of you directly nor your name, the love that it brings to them and they send back out in the world will flow to you at some point as well. So rather than having someone spot you at work and come to shake your hand, you will get love in the future courtesy of those lovers of natural beauty you have helped to continue receiving that great reward of divine awareness that nature brings. You and they will all be blessed and will share the benefits.
The answer for those who are out of alignment is healing and this you are contributing to as well, so take heart, you are bringing the answer you seek through your own efforts and that is in keeping with Creator’s Plan, that it is up to humans to save themselves even from the thoughtlessness of others including major acts of evil brought by interlopers. In effect, you are tapping into the divine, that is the impulse you are bringing to bear here in your desire to improve the environment if only to the human eye. That has benefits beyond a simple appreciation of an uncluttered environment for a brief time by an observer. When love flows, it does many things, has many benefits, and will touch many hearts. In a sense, you are keeping the lifeblood of humanity going because it is fueled and carried by love as energy because that is the purpose of humanity to begin with. Anything that is non-divine slows the flow, so the impact is greater than it seems on the surface, of your kindness.